what's wrong with my Chrony? AGH!!!

[Tippet]

Shooting today, I chronied my 90 gr Hornady XTP HP .380 loads at an average of 865 or so, using medium-charge weight of HP-38. OK Then the AR, Speer 55 gr fmj's with Varget at 3100. So far so good. But then the 9mm: 124 gr Hornady XTP HP's with medium charge weights of HP-38 were showing around 1950 FPS!!?? seems like about twice what they ought to be, but no high pressure signs and in fact they felt not like they were hot loads, but rather they felt like light loads.

What is going on? I'd assume the chrony is whacked, but the other ones were right where I expected them to be.

[StarMetal]

Shooting today, I chronied my 90 gr Hornady XTP HP .380 loads at an average of 865 or so, using medium-charge weight of HP-38. OK Then the AR, Speer 55 gr fmj's with Varget at 3100. So far so good. But then the 9mm: 124 gr Hornady XTP HP's with medium charge weights of HP-38 were showing around 1950 FPS!!?? seems like about twice what they ought to be, but no high pressure signs and in fact they felt not like they were hot loads, but rather they felt like light loads.

What is going on? I'd assume the chrony is whacked, but the other ones were right where I expected them to be.

Standing to close to the chrono..maybe picking up the muzzle flash. Bright sun reflection too much off the bullets. Who knows.

Joe

[rickster]

Yep. I've had that happen when I was too close.

[Ricochet]

If you're really close, the muzzle blast or its shock wave can still be outracing the bullet.

[Tippet]

I wasn't "really" close, no closer than with the 380 or the AR15

[Mavrick]

I've had the same thing happen...Can you imagine 4200fps(!!!) from a 6" M57?
I use an Oehler M33 with a 5' split and a 5' first screen.
With mine it wouldn't do it every time, but it seemed to be the angle of the sun, and it happens every year, so, at THAT range, I quit using the chronograph from November to March.
I used to place the computer on the bench, and the handguns gave a lot of trouble when the loads got hotter, so now put in on it's own seat behind me. The noise(vibration) seemed to cause the chip(or batteries) to "stutter" and read high.
Have fun,
Gene

[HammerMTB]

I've had the same thing happen...Can you imagine 4200fps(!!!) from a 6" M57?


Or how about 7000 FPS from a SRH .44 Mag? THAT was a surprise! :shock:
In my case, it was a close by hi voltage power wire from the BPA.
Curiously, it did not do this all the time, but intermittently, most of all when the humidity was high.
I have had muzzle blast skew readings, too. Got a 2000+FPS reading from a .45 Colt Blackhawk yesterday. I'm certain that 255 gr slug was NOT traveling that fast.
These days I try to keep my screens 5-8 feet downrange. That seems to be enough for all but the smokepole.
Your Chrony will have a troubleshooting tree. Follow it and I bet you will find the cause.

[Tippet]

yes I worked through the troubleshooting guide before I posted. I guess it must have been the angle of the sun combined with shiny bullets. As I said the other calibers tested as expected and I was a good 10' from the chrony.

[Ricochet]

Perhaps the bullet shadow tripping the first screen and a reflection off of the bullet tripping the second before the bullet got there.

[Tippet]

That must be it exactly Ricochet I can;'r figure any other way. I'll have a chance to get out again in a few days we'll see if different conditions bring differerent results.

[wiljen]

Paint the bullets black with a sharpie then try em again. Sometimes cutting down the reflective surface will cure that error in bright sunlight conditions.